Seaweed-Derived Route to Fe2O3 Hollow ... - ACS Publications

Research Article www.acsami.org

Seaweed-Derived Route to Fe2O3 Hollow Nanoparticles/N-Doped Graphene Aerogels with High Lithium Ion Storage Performance Long Liu,†,# Xianfeng Yang,‡,# Chunxiao Lv,† Aimei Zhu,† Xiaoyi Zhu,† Shaojun Guo,*,⊥ Chengmeng Chen,∥ and Dongjiang Yang*,†,§ †

Collaborative Innovation Center for Marine Biomass Fibers, Materials and Textiles of Shandong Province, School of Environmental Science and Engineering, Qingdao University, Qingdao 266071, China ‡ Analytical and Testing Center, South China University of Technology, Guangzhou 510640, China ⊥ Department of Materials Science and Engineering and Department of Energy and Resources Engineering, College of Engineering, Peking University, Beijing 100871, China § Queensland Micro- and Nanotechnology Centre (QMNC), Griffith University, Nathan, Brisbane, Queensland 4111, Australia ∥ Key Laboratory of Carbon Materials, Institute of Coal Chemistry, Chinese Academy of Sciences, Taiyuan 030001, China S Supporting Information *

ABSTRACT: We developed a nanoscale Kirkendall effect assisted method for simple and scalable synthesis of three-dimensional (3D) Fe2O3 hollow nanoparticles (NPs)/graphene aerogel through the use of waste seaweed biomass as new precursors. The Fe2O3 hollow nanoparticles with an average shell thickness of ∼6 nm are distributed on 3D graphene aerogel, and also act as spacers to make the separation of the neighboring graphene nanosheets. The graphene−Fe2O3 aerogels exhibit high rate capability (550 mA h g−1 at 5 A g −1) and excellent cyclic stability (729 mA h g−1 at 0.1 A g−1 for 300 cycles), outperforming all of the reported Fe2O3/graphene hybrid electrodes, due to the hollow structure of the active Fe2O3 NPs and the unique structure of the 3D graphene aerogel framework. The present work represents an important step toward high-level control of high-performance 3D graphene−Fe-based NPs aerogels for maximizing lithium storage with new horizons for important fundamental and technological applications. KEYWORDS: seaweed, egg box, Kirkendall effect, hollow nanoparticles, lithium ion batteries

■

INTRODUCTION A severe challenge is facing scientists to develop new anode materials for lithium ion batteries (LIBs) which have good rate capability, excellent long-term cycle life, and high energy density. The traditional graphite cannot satisfy the increasing demands for LIBs anode materials because of its low theoretical capacity (372 mA h g−1). Alternative anodes including semiconductor or metal oxides, which have high theoretical capacities (such as Si of 4200 mA h g−1; Fe2O3 of 1007 mA h g−1), have been synthesized to replace the graphitic carbon materials. Unfortunately, these materials such as Fe2O3 and Si always are afflicted with serious capacity decay resulting from large volume expansion in the lithiation process. Recently, it was reported that loading sufficient void space to adapt the volumetric change is of vital significance to the prolonged cycling stability because the hollow structures can facilitate the Li+ transport in the host matrix by providing larger surface area and shorten solid-state diffusion length.1,2 Since then, many attempts have been focused on the synthesis of various hollow nanostructures by Ostwald ripening,3 electron-beam irradiation,4 the hydrothermal method,5 and solvothermal reaction.6 However, because of their complicated multistep fabricating process, the existed methods are time-consuming, and both the © 2016 American Chemical Society

yield and crystalline degree of the obtained hollow nanoparticles are low. The lately reported nanoscale Kirkendall effect-assisted method, generally ascribed to the outward diffusion of cationic species, shows great potential for template-free fabrication of hollow nanoparticles.7−9 It is well-known that high-performance battery materials require not only high surface area but also a good electrical conductive network. Graphene aerogels (GAs) are unique discovered materials with high surface area and electrical conductivity. Compared with other porous carbon materials, GAs have significant advantages such as hierarchical threedimensional (3D) morphology and adjustable surface area and pore size distributions. These merits, particularly the interconnected macropores (>50 nm), make GAs attractive for devices that need large surface areas and rapid mass transport, for example, a support to load metal nanoparticles (NPs) for energy conversion and storage applications.10 Herein, we report a simple, sustainable, and scalable way to prepare 3D Fe2O3 hollow nanoparticles/N-doped graphene Received: December 19, 2015 Accepted: March 4, 2016 Published: March 4, 2016 7047

DOI: 10.1021/acsami.5b12427 ACS Appl. Mater. Interfaces 2016, 8, 7047−7053

Research Article

ACS Applied Materials & Interfaces

Figure 1. Schematic description for the controllable preparation of high-performance energy nanomaterials. (a) The fabrication of Fe2N@C-NPs/NGAs obtained from SA/graphene gelation and (b) conversion process from Fe2N@C-NPs/N-GAs to Fe2O3−HNPs/N-GAs.

hybrid aerogels (Fe2O3−HNPs/N-GAs) using seaweed-derived biomass conversion strategy. The key feature for our synthesis involves the use of the novel “egg-box” structure of Fe-alginate which serves as new precursors for making hybrid aerogels. After calcination at 700 °C in the presence of NH3, the 3D Fealginate/graphene aerogels can be converted to core@shell Fe2N@C-NPs/N-GAs. Then the core@shell Fe2N@C-NPs were converted to Fe2O3−HNPs with shell thickness of ∼6 nm after thermal treatment in air via typical nanoscale Kirkendall effect-assisted process. Our new hybrid aerogels deliver high reversible capacity of 1483 mA h g−1 at 0.1 A g−1, excellent rate capacity (550 mA h g−1 at even 5 A g −1), and prolonged cycling life (maintaining 729 mA h g−1 at 0.1 A g−1 for 300 cycles) for lithium ion storage. As far as we know, the present Fe2O3−HNPs/N-GAs are the most efficient Fe2O3-based anode materials ever reported for LIBs.

■

80:10:10 and calendered on a copper foil to fabricate the working electrode. The loading amount of active material is ∼0.61 mg cm−2. CR2016 coin-type cells were assembled and tested according to our previous reports.16−19

■

RESULTS AND DISCUSSION Figure 1 shows the synthesis process for Fe2O3−HNPs/N-GAs. First, we mixed natural sodium alginate (SA) with various amounts of graphene to obtain SA/graphene hybrid collosol, and then poured them into a FeCl3 liquid at room temperature. Here, the SA/graphene collosol can be converted to hydrogel11,20,21 because of the formation of an egg-box structure by a chelation reaction between Fe3+ anions and four G-blocks of SA. The bulky hydrogels were freeze-dried to obtain 3D Fealginate/graphene aerogels. The size of the hybrid aerogel is controlled only by the volume of a container. The 3D Fealginate/graphene aerogels were calcined at 700 °C in the presence of NH3 to convert to Fe2N@C-NPs/N-GAs (see XRD pattern in Figure S1a, Supporting Infromation), where the Fe-alginate egg-box can be transferred to a core@shell Fe2N@C-NPs since the Fe3+ ions were confined within the alginate egg box before carbonization (Figure 1a and Figure S1b−d). Through typical nanoscale Kirkendall effect, the Fe2N@C-NPs/N-GAs were oxidized at 400 °C in air to obtain Fe2O3−HNPs/N-GAs (Figure 1b). During the conversion process, the core Fe2N NPs diffuse into the outside carbon shell gradually and in the meantime an inward diffusion of O2 into the carbon shell occurs, where the carbon shell offers diffusion vacancies and regulates the interdiffusion rates of Fe2N and O2.9 Therefore, the inward vacancy diffusion took place from the carbon shell with the gradual disappearance of the Fe2N core, and a full hollow structure was formed when the Fe2N core diffused into the carbon shell completely. Then the Fe2N NPs in the carbon shell were fully oxidized to high-crystalline α-Fe2O3 by long-time thermal treatment in air, accompanied by the complete consumption of carbon and nitrogen in the amorphous carbon shell. The TGA curve of Fe2N@C-NPs/NGAs-10 was shown in Figure S2. The small weight increases at 80−200 and 300−350 °C, corresponding to the oxidation process of Fe2N NPs, and the abrupt weight loss between 270 and 310 °C was probably ascribed to the consumption of amorphous carbon shell. The N-doped GAs can be decomposed when the temperature is higher than 400 °C.

EXPERIMENTAL SECTION

Characterizations. The morphology, chemical composition, structure analysis, and specific surface areas of the aerogel samples were thoroughly studied by using field emission scanning electron microscopy (FE-SEM), high-resolution transmission electron microscopy (HRTEM), high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), thermogravimetric analysis (TGA), water contact angle analysis, Raman analysis, N2 adsorption method, and methylene blue (MB) adsorption method, respectively. Detailed characterization has been explained in our previous work.11−15 Synthesis of Fe2N@C-NPs/N-GAs-x. A 1 wt % alginate (Aladdin Chemistry Co. Ltd. ⩾99.0%) solution with different amounts of graphene (x = 0, 5, 10, 20; mass ratio (%) of graphene/sodium alginate) was poured into a 2.5 wt % FeCl3·6H2O (Aladdin Chemistry Co. Ltd., Shanghai, China, ⩾99.0%) aqueous solution under vigorous stirring to form Fe-alginate/graphene hydrogel. The as-prepared hybrid gels were dehydrated through the freeze-drying process to obtain three-dimensional Fe-alginate/graphene aerogels (FeA/GAs).11 The resultant FeA/GAs composite was treated at 250 °C in a nitrogen atmosphere for 1 h and heated to 700 °C for 2 h with the heating rate of 5 °C min−1 in ammonia gas. Synthesis of Fe2O3−HNPs/N-GAs-x. In a typical synthesis, the Fe2N@C-NPs/N-GAs-x samples were treated at 400 °C for 2 h in air atmosphere, and the Fe2O3−HNPs/N-GAs-x samples were obtained after cooling to room temperature naturally. LIB Measurements. The aerogel powder, acetylene black, and polyvinylidene fluoride (PVDF) were mixed at a weight ratio of 7048


Research Article


Figure 2. Structural characterization of Fe2O3−HNPs/N-GAs. (a) XRD patterns; (b) Raman spectra of Fe2O3−HNPs/N-GAs-x and support-free Fe2O3; (c) DTA/TG thermal analysis of Fe2O3−HNPs/N-GAs-10; (d) XPS survey spectra of the Fe2O3−HNPs/N-GAs-10 and high resolution XPS spectra of Fe2O3−HNPs/N-GAs-10; (e) Fe 2p and (f) N 1s peak.

Figure 2a shows the XRD analysis of Fe2O3−HNPs/N-GAs-x composites, which reveals that the obtained products are αFe2O3 (JCPDS No. 33−0664). Interestingly, the graphitic diffraction peak at 20−30° could not be identified, illustrating that Fe2O3 HNPs were efficiently anchored on the surface of graphene, suppressing the agglomeration of graphene layers.10 Raman spectra of Fe2O3−HNPs/N-GAs-x show both the characteristic peaks of α-Fe2O3 (A1g: 214 and 474 cm−1; Eg: 273, 384, and 583 cm−1)22 and the D and G peaks of graphene (Figure 2b). Furthermore, the ID/IG of Fe2O3−HNPs/N-GAs5, Fe2O3−HNPs/N-GAs-10, and Fe2O3−HNPs/N-GAs-20 are 1.06, 0.97, and 0.95, respectively, indicating the improvement in the degree of graphitic crystalline structure by the addition of the graphene content.23 Thermal gravimetric (TG) analysis and differential thermal analysis (DTA) of Fe2O3−HNPs/N-GAs10 reveal that a prominent endothermic peak appears at 460 °C, which refers to the decomposition of N-GAs support (∼14 wt %) (Figure 2c). The XPS full-scan spectrum shows the principal C 1s, O 1s, N 1s, and Fe 2p core levels (Figure 2d). By comparing the peak intensity of N 1s between Fe2O3− HNPs/N-GAs and Fe2N@C-NPs/N-GAs, we found that the oxidation annealing could affect the overall N content, whereas Fe2O3−HNPs/N-GAs lost most of the original N content (N, 0.6 at. %) compared to Fe2N@C-NPs/N-GAs (N, 9.49 at. %) (Table S1). This is due to the oxidation annealing process consuming the N-doped amorphous carbon on the surface of Fe2O3 hollow NPs. The high-resolution XPS spectra with curve fitting indicate that the C 1s spectra of Fe2O3−HNPs/N-GAs has a graphitic C−C peak at 284.8 eV, together with C−N (286.3 eV) and CO (288.8 eV) (Figure S3a).24 The O 1s spectrum can be deconvoluted into four O species, which are centered at 530, 531.9, 533.4, and 535.0 eV, respectively. Remarkably, a new peak corresponding to O2− of Fe2O3 can be observed at 530 eV after oxidation annealing treatment (Figure S3b).25 The XPS survey spectrum shows typical characteristic

peaks of Fe2O3 at 711 and 725 eV, referring to Fe 2p3/2 and Fe 2p1/2,22,26 respectively. The Fe 2p3/2 and Fe 2p1/2 main peaks with two satellite peaks on their high binding-energy side (∼8 eV) are shown in Figure 2e, implying the characteristic peaks of Fe2O3.22 A small amount of residual nitrogen was detected in the Fe2O3−HNPs/N-GAs after Kirkendall effect-assisted process. The high-resolution N 1s spectrum can be well-fitted by three peaks: pyridinic-N (398.3 eV), pyrrolic-N (400.3 eV), and graphitic-N (402.7 eV)27 (Figure 2f). Theoretical and experimental studies illustrate that N-doping can lower the energy barrier of lithium insertion and increase reactive sites, and thus enhance the lithium storage properties, compared to undoped graphene.27,28 N2 adsorption/desorption isotherms and pore size distributions (PSDs) of Fe2O3−HNPs/N-GAs-x are shown in Figure 3. The BET specific surface areas of Fe2O3−HNPs/N-GAs-x range from 71 to 436 m2/g, and typical bimodal PSDs were

Figure 3. Brunauer−Emmett−Teller (BET) specific surface areas of the samples. (a) N2 adsorption/desorption isotherms and (b) pore size distributions of Fe2O3−HNPs/N-GAs-x (x = 0, 5, 10, and 20) and support-free Fe2O3. 7049


Research Article


Table 1. (a) Gravimetric and (b) Volumetric Specific Surface Areas of Fe2O3−HNPs/N-GAs-x (x = 5, 10, 20, Mass Ratio x% of Graphene) Measured by MB Adsorption sample

MFe2O3‑HNPs/N‑GAs‑x (mg)

VFe2O3‑HNPs/N‑GAs‑x (cm3)

ΔMMB (mg)

gravimetric SSA (m2 g−1)

volumetric SSA (m2 cm−3)

Fe2O3−HNPs/N-GAs-5 Fe2O3−HNPs/N-GAs-10 Fe2O3−HNPs/N-GAs-20

9.3 8.5 6.1

0.5 0.5 0.5

0.3 0.6 1.1

82 179 461

0.41 0.72 1.45

difference between the core and border are relatively uniformly anchored on the graphene. Furthermore, the elemental mapping (Figure 4g) result shows that in addition to a small amount of residual nitrogen, almost no amorphous carbon (AC) was left, indicating the carbon-encapsulated Fe2Ns NPs were sufficiently converted to Fe2O3 HNPs. On the basis of the above discussion, we concluded that the N-AC shellencapsulated Fe2N NPs core supported on graphene have completely been converted to Fe2O3 HNPs/graphene (Figure 4b). The electrochemical and LIB property of Fe2O3−HNPs/NGAs-x were analyzed by cyclic votalmmograms (CV) and galvanostatic cycling. Figure 5a shows the CV of Fe2O3− HNPs/N-GAs-10 in the voltage range of 0.01−3.00 V. In the first cathodic scan, the peak at 0.6 V is attributed to the solidelectrolyte-interphase (SEI) film and other side reactions. The peak disappears in the following cycles and transfers to a peak at 0.9 V, which can be attributed to the reversible insertion of lithium ions and complete reduction of FeO to Fe(0).30 Two overlapping anodic peaks between 1.5 and 2.0 V in the first cycle is also observed, which can be ascribed to the oxidation of Fe to Fe2+ and further oxidation to Fe3+ (2FeO + 2Li2O → Fe2O3 + 4Li+ + 4e−).31 The capacity versus voltage curves of Fe2O3−HNPs/N-GAs-10 at the 1st, 2nd, 30th, 50th, 80th, and 100th cycles at 0.1 A g−1 with a voltage range between 3.0 and 0.01 V are plotted in Figure 5b. A reversible charge capacity of 1016 mA h g−1 with a relatively low irreversible capacity loss of 36% are observed. The irreversible loss of the capacity can be ascribed to irreversible processes like the formation of SEI film or the decomposition of the electrolyte.30,32 After the second cycle, the capacity of Fe2O3−HNPs/N-GAs-10 increases gradually from 1070 to 1483 mA h g−1 within 100 cycles (Figure 5b). Such activated process for nanostructured Fe2O3 materials may be caused by loss of crystallinity of the Fe2O3− HNPs or their transformation to an amorphous-like structure in the circulation’s process, hence enhancing the Li diffusion kinetics.31,33 This phenomenon may also be ascribed to the growth of a gel-like polymeric film that can enhance the mechanical cohesion of catalyst and release the excess capacity at low voltage (so-called “pseudo-capacitance-type behavior”).31,34 Moreover, the increased reversible capacity is probably ascribed to the doping of nitrogen in the GAs (Figure 2f), which could significantly boost the capacity of the GAs and lower the possibility of electrolyte decomposition and irreversible lithium insertion because of the pulverization of carbon.28 The capacity and cyclic stability were used to evaluate the lithium storage performance of the Fe2O3−HNPs/N-GAs-10 electrode. Fe2O3−HNPs/N-GAs-10 with ∼86% mass ratio of active Fe2O3 HNPs exhibits a high reversible capacity of 1483 mA h g−1 at 0.1 A g−1 (1.5 times the theoretical capacity of αFe2O3) and a gradually increased stability during cycling with high Coulombic efficiency around 95−99% (Figure 5c). The increased measured capacity during cycling is consistent with the galvanostatic charge−discharge profile mentioned above.

investigated by employing the Barrett−Joyner−Halenda (BJH) model. Large mesopores (∼30 nm) are ascribed to the 3D porous aerogel network, and small ∼3 nm mesopores are due to the thermal decomposition of the alginate precursors.11,17−19,29 Furthermore, the specific surface areas of Fe2O3−HNPs/N-GAs-x were tested by MB absorption analysis (Figure S4). Table 1 shows that the specific surface areas calculated from MB absorption analysis range from 82 to 461 m2 g−1, which are slightly higher than those of BET results. This phenomenon has been found in other GA materials, of which the macropores can be accurately tested by MB sorption analysis.11 Thus, the 3D porous network of GA contributes to a higher specific surface area. The TEM (Figure 4a) and FE-SEM (Figure S5a) images of Fe2O3−HNPs/N-GAs-10 show that Fe2O3 HNPs were

Figure 4. Morphology and structural characterization of Fe2O3− HNPs/N-GAs-10. (a) TEM image of Fe2O3−HNPs/N-GAs-10 (Inset: an enlarged view of a typical HNP). (b) The model structure of Fe2O3−HNPs/N-GAs-x. (c) SAED images, (d) HRTEM pattern (inset: the FFT image), (e) IFFT pattern, (f) energy-dispersive X-ray and HAADF-STEM images, and (g) element mapping patterns (C, O, N, and Fe) of Fe2O3−HNPs/N-GAs-10.

homogeneously distributed on the N-GAs, even via an oxidation annealing treatment. A regular diffraction spot ring is observed from the selected-area electron diffraction (SAED) pattern (Figure 4c), indicating the polycrystalline structure of the Fe2O3−HNPs. These Fe2O3 HNPs have an average shell thickness of ∼6 nm (Figure 4d). The inverse fast Fourier transform (IFFT) image (Figure 4e) selected in the HRTEM image reveals distinct lattice fringes, which are assigned to 0.22, 0.27, and 0.37 nm, corresponding to the (113), (104), and (012) planes of α-Fe2O3. The HAADF-STEM image (Figure 4f) demonstrates that the Fe2O3−HNPs with the contrast 7050


Research Article


Figure 5. LIB performance of Fe2O3−HNPs/N-GAs-x. (a) CV of Fe2O3−HNPs/N-GAs-10 at 0.1 mV s−1. (b) Galvanostatic charge−discharge profile of Fe2O3−HNPs/N-GAs-10 at 0.1 A g−1. (c) Long-term cycle of Fe2O3−HNPs/N-GAs-10 at 0.1 A g−1. (d) Comparison of rate performance of Fe2O3−HNPs/N-GAs-5, Fe2O3−HNPs/N-GAs-10, and Fe2O3−HNPs/N-GAs-20. (e) Comparison of the cycling ability of Fe2O3−HNPs/NGAs-5, Fe2O3−HNPs/N-GAs-10, and Fe2O3−HNPs/N-GAs-20 at 1 A g−1.

capability (550 mA h g−1 at even 5 A g−1, Figure 5d) and cyclability (maintaining 729 mA h g−1 for 300 cycles at 0.1 A g−1, Figure 5e) compared to Fe2O3−HNPs/N-GAs-20 and Fe2O3−HNPs/N-GAs-5, indicating the proper surface area, electron conductivity, and active site density have a strong impact on facilitating rapid electrochemical kinetics, low internal resistance, and rapid charge transfer. As for anode material in LIBs, the peculiar structure of Fe2O3−HNPs/N-GAs contributes to the high performance. As illustrated in Figure 6, the outstanding cycling stability and remarkably high rate capability of the Fe2O3−HNPs/N-GAs can be attributed to the synergetic effect of the Fe2O3 hollow structure and the flexible graphene backbone. (1) The Fe2O3 HNPs supported on GAs form a hierarchical 3D mass transportation pathway, facilitating the transportation of the electrolyte and Li+ within the electrode. (2) The GAs structure can be easily infiltrated by water molecules to make liquid electrolyte contact more graphene edges and surfaces. Also, as

However, the commercial Fe2O3 HNPs exhibit faster capacity decaying with only 257 mA h g−1 left after 100 cycles (Figure S6). Besides, to evaluate the rate performance, the Fe2O3− HNPs/N-GAs-10 was cycled at different current densities ranging within 0.1 to 5 A g−1. As shown in Figure 5d, the composite delivers the specific capacity of 902, 813, 746, 656, and 550 mA h g−1 at 0.2, 0.5, 1, 2, and 5 A g−1, respectively. A reversible capacity of 1100 mA h g−1 can be received once the current density rebounds back to 0.1 A g−1 after 60 cycles. Most notably, the cyclability and rate performance of Fe2O3−HNPs/ N-GAs are better than most of the lately reported Fe2O3-based anode materials,8,30−32,35−45 such as α-Fe2O3 hollow spheres, Fe2O3/GAs, hierarchical Fe2O3 microboxes, and Fe2O3@PANi (Table S2). It should be noted that the initial doped graphene content has a profound influence on the lithium storage capacities and rate performance of Fe2O3−HNPs/N-GAs-x. As shown in Figure 5, Fe2O3−HNPs/N-GAs-10 shows the best rate 7051


Research Article


■

(Figure S3), methlylene blue (MB) adsorption spectra (Figure S4), FE-SEM image of the as-synthesized Fe2O3−HNPs/N-GAs with and without graphene (Figure S5), cycling performance of commercial Fe2O3 NPs (Figure S6), electrochemical impedance spectroscopy of obtained samples (Figure S7), elemental composition of as-received composites (Table S1), and the comparison of the LIBs performance with recently reported Fe2O3-based materials (Table S2) (PDF)

AUTHOR INFORMATION

Corresponding Authors

Figure 6. Materials architectures and schematic diagram of enhanced Li ion-exchange process on Fe2O3−HNPs/N-GAs.

*E-mail: [email protected] (S.G.). *E-mail: [email protected] (D.Y.).

shown in Figure 7, the wettability of Fe2O3−HNPs/N-GAs is probed with a Theta/Attension optical tensiometer. It reveals

Author Contributions #

These authors contributed equally to this work.

Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS This work is financially supported by the National Natural Science Foundation of China (No. 51503109, 21501105, and 51473081), start-up funding from Peking University, Young Thousand Talented Program, and ARC Discovery Project (No. 130104759), and the Fundamental Research Funds for the Central Universities (Grant No. 20152M058).

Figure 7. Contact angles of (a) Fe2O3−HNPs/N-GAs and (b) support-free Fe2O3.

■

that the GAs film is highly hydrophilic in nature with a small contact angle of 57°, in contrast to 96° for support-free Fe2O3. (3) The flexible graphene can improve the electrical conductivity by forming a conductive network. (The electrontransfer resistance of Fe2O3−HNPs/N-GAs is only 28 Ω, as shown in Figure S7) It can also stabilize the whole structure by preventing the pulverization of Fe2O3,32,38 and avoid the aggregation of the Fe2O3 HNPs during the cell cycle.46 (4) The hollow structure is efficient at avoiding the dramatic volume changes of Fe2O3 upon cycling, and accommodate the mechanical stresses associated with the lithium charging− discharging process. Furthermore, the small size of Fe2O3 HNPs can dramatically shorten the ionic diffusion.

■

CONCLUSIONS To summarize, we demonstrate a new biomass conversion strategy for scalable and sustainable synthesis of the Fe2O3 HNPs-3D N-graphene hybrid aerogels via the novel nanoscale Kirkendall effect derived from alginate hydrogel. It shows high reversible capacity of about 1483 mA h g−1 at 0.1 A g−1 up to 100 cycles, good rate performance, and excellent cycling ability. The present work opens a new opportunity in exploring a very simple, economic, and ecofriendly biomass conversion route to fabricate future high-performance energy material for LIBs.

■

REFERENCES

(1) Lee, K. T.; Lytle, J. C.; Ergang, N. S.; Oh, S. M.; Stein, A. Synthesis and Rate Performance of Monolithic Macroporous Carbon Electrodes for Lithium-Ion Secondary Batteries. Adv. Funct. Mater. 2005, 15, 547−556. (2) Wang, Y.; Su, F.; Lee, J. Y.; Zhao, X. Crystalline Carbon Hollow Spheres, Crystalline Carbon-SnO2 Hollow Spheres, and Crystalline SnO2 Hollow Spheres: Synthesis and Performance in Reversible Li-Ion Storage. Chem. Mater. 2006, 18, 1347−1353. (3) Yang, H. G.; Zeng, H. C. Self-Construction of Hollow SnO2 Octahedra Based on Two-Dimensional Aggregation of Nanocrystallites. Angew. Chem. 2004, 116, 6056−6059. (4) Latham, A. H.; Wilson, M. J.; Schiffer, P.; Williams, M. E. TEMInduced Structural Evolution in Amorphous Fe Oxide Nanoparticles. J. Am. Chem. Soc. 2006, 128, 12632−12633. (5) Li, L.; Chu, Y.; Liu, Y.; Dong, L. Template-Free Synthesis and Photocatalytic Properties of Novel Fe2O3 Hollow Spheres. J. Phys. Chem. C 2007, 111, 2123−2127. (6) Wu, Z.; Yu, K.; Zhang, S.; Xie, Y. Hematite Hollow Spheres with a Mesoporous Shell: Controlled Synthesis and Applications in Gas Sensor and Lithium Ion Batteries. J. Phys. Chem. C 2008, 112, 11307− 11313. (7) Yin, Y.; Rioux, R. M.; Erdonmez, C. K.; Hughes, S.; Somorjai, G. A.; Alivisatos, A. P. Formation of Hollow Nanocrystals through the Nanoscale Kirkendall Effect. Science 2004, 304, 711−714. (8) Zhou, J.; Song, H.; Chen, X.; Zhi, L.; Yang, S.; Huo, J.; Yang, W. Carbon-Encapsulated Metal Oxide Hollow Nanoparticles and Metal Oxide Hollow Nanoparticles: a General Synthesis Strategy and Its Application to Lithium-Ion Batteries. Chem. Mater. 2009, 21, 2935− 2940. (9) Zhou, J.; Song, H.; Chen, X.; Zhi, L.; Huo, J.; Cheng, B. Oxidation Conversion of Carbon-Encapsulated Metal Nanoparticles to Hollow Nanoparticles. Chem. Mater. 2009, 21, 3730−3737. (10) Wu, Z.-S.; Yang, S.; Sun, Y.; Parvez, K.; Feng, X.; Müllen, K. 3D Nitrogen-Doped Graphene Aerogel-Supported Fe3O4 Nanoparticles as Efficient Electrocatalysts for the Oxygen Reduction Reaction. J. Am. Chem. Soc. 2012, 134, 9082−9085.

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsami.5b12427. XRD pattern, FE-SEM image, and TEM image of Fe2N@ C-NPs/N-GAs (Figure S1), TG analysis of Fe2N@CNPs/GAs-10 (Figure S2), high-resolution XPS spectra 7052


Research Article

ACS Applied Materials & Interfaces (11) Liu, L.; Yang, X.; Ma, N.; Liu, H.; Xia, Y.; Chen, C.; Yang, D.; Yao, X. Scalable and Cost-Effective Synthesis of Highly Efficient Fe2NBased Oxygen Reduction Catalyst Derived from Seaweed Biomass. Small 2016, 12, 1295−1301. (12) Chen, S.; Duan, J.; Tang, Y.; Jin, B.; Zhang Qiao, S. Molybdenum Sulfide Clusters-Nitrogen-Doped Graphene Hybrid Hydrogel Film as an Efficient Three-Dimensional Hydrogen Evolution Electrocatalyst. Nano Energy 2015, 11, 11−18. (13) Chen, J.; Sheng, K.; Luo, P.; Li, C.; Shi, G. Graphene Hydrogels Deposited in Nickel Foams for High-Rate Electrochemical Capacitors. Adv. Mater. 2012, 24, 4569−4573. (14) Li, Y.; Chen, J.; Huang, L.; Li, C.; Hong, J. D.; Shi, G. Highly Compressible Macroporous Graphene Monoliths via an Improved Hydrothermal Process. Adv. Mater. 2014, 26, 4789−4793. (15) McAllister, M. J.; Li, J.-L.; Adamson, D. H.; Schniepp, H. C.; Abdala, A. A.; Liu, J.; Herrera-Alonso, M.; Milius, D. L.; Car, R.; Prud’homme, R. K.; Aksay, I. A. Single Sheet Functionalized Graphene by Oxidation and Thermal Expansion of Graphite. Chem. Mater. 2007, 19, 4396−4404. (16) Sun, J.; Li, D.; Xia, Y.; Zhu, X.; Zong, L.; Ji, Q.; Jia, Y. A.; Yang, D. Co3O4 Nanoparticle Embedded Carbonaceous Fibres: A Nanoconfinement Effect on Enhanced Lithium-Ion Storage. Chem. Commun. 2015, 51, 16267−16270. (17) Li, D.; Yang, D.; Zhu, X.; Jing, D.; Xia, Y.; Ji, Q.; Cai, R.; Li, H.; Che, Y. Simple Pyrolysis of Cobalt Alginate Fibres into Co3O4/C Nano/Microstructures for a High-performance Lithium Ion Battery Anode. J. Mater. Chem. A 2014, 2, 18761−18766. (18) Li, D.; Lv, C.; Liu, L.; Xia, Y.; She, X.; Guo, S.; Yang, D. Egg-Box Structure in Cobalt Alginate: A New Approach to Multifunctional Hierarchical Mesoporous N-Doped Carbon Nanofibers for Efficient Catalysis and Energy Storage. ACS Cent. Sci. 2015, 1, 261−269. (19) Lv, C.; Yang, X.; Umar, A.; Xia, Y.; Jia, Y. A.; Shang, L.; Zhang, T.; Yang, D. Architecture-Controlled Synthesis of MxOy (M= Ni, Fe, Cu) Microfibres from Seaweed Biomass for High-Performance Lithium Ion Battery Anodes. J. Mater. Chem. A 2015, 3, 22708−22715. (20) Nakamura, K.; Nishimura, Y.; Hatakeyama, T.; Hatakeyama, H. Thermal Properties of Water Insoluble Alginate Films Containing Diand Trivalent Cations. Thermochim. Acta 1995, 267, 343−353. (21) Dong, Y.; Dong, W.; Cao, Y.; Han, Z.; Ding, Z. Preparation and Catalytic Activity of Fe Alginate Gel Beads for Oxidative Degradation of Azo Dyes Under Visible Light Irradiation. Catal. Today 2011, 175, 346−355. (22) Nasibulin, A. G.; Rackauskas, S.; Jiang, H.; Tian, Y.; Mudimela, P. R.; Shandakov, S. D.; Nasibulina, L. I.; Jani, S.; Kauppinen, E. I. Simple and Rapid Synthesis of α-Fe2O3 Nanowires under Ambient Conditions. Nano Res. 2009, 2, 373−379. (23) Li, Y.; Zhou, W.; Wang, H.; Xie, L.; Liang, Y.; Wei, F.; Idrobo, J.-C.; Pennycook, S. J.; Dai, H. An Oxygen Reduction Electrocatalyst Based on Carbon Nanotube-Graphene Complexes. Nat. Nanotechnol. 2012, 7, 394−400. (24) Shang, N. G.; Papakonstantinou, P.; McMullan, M.; Chu, M.; Stamboulis, A.; Potenza, A.; Dhesi, S. S.; Marchetto, H. Catalyst-Free Efficient Growth, Orientation and Biosensing Properties of Multilayer Graphene Nanoflake Films with Sharp Edge Planes. Adv. Funct. Mater. 2008, 18, 3506−3514. (25) Srivastava, H.; Tiwari, P.; Srivastava, A.; Nandedkar, R. Growth and Characterization of α-Fe2O3 Nanowires. J. Appl. Phys. 2007, 102, 054303. (26) Xin, J.; Jia-jia, C.; Jian-hui, X.; Yi-ning, S.; You-zuo, F.; Min-sen, Z.; Quan-feng, D. Fe2O3 Xerogel Used as the Anode Material for Lithium Ion Batteries with Excellent Electrochemical Performance. Chem. Commun. 2012, 48, 7410−7412. (27) Reddy, A. L. M.; Srivastava, A.; Gowda, S. R.; Gullapalli, H.; Dubey, M.; Ajayan, P. M. Synthesis of Nitrogen-Doped Graphene Films for Lithium Battery Application. ACS Nano 2010, 4, 6337−6342. (28) Li, X.; Zhu, X.; Zhu, Y.; Yuan, Z.; Si, L.; Qian, Y. Porous Nitrogen-Doped Carbon Vegetable-Sponges with Enhanced Lithium Storage Performance. Carbon 2014, 69, 515−524.

(29) Zhao, W.; Yuan, P.; She, X.; Xia, Y.; Komarneni, S.; Xi, K.; Che, Y.; Yao, X.; Yang, D. Sustainable Seaweed-Based One-Dimensional (1D) Nanofibers as High-Performance Electrocatalysts for Fuel Cells. J. Mater. Chem. A 2015, 3, 14188−14194. (30) Wang, Z.; Luan, D.; Madhavi, S.; Hu, Y.; Lou, X. W. Assembling Carbon-Coated α-Fe2O3 Hollow Nanohorns on the CNT Backbone for Superior Lithium Storage Capability. Energy Environ. Sci. 2012, 5, 5252−5256. (31) Lin, J.; Raji, A. R. O.; Nan, K.; Peng, Z.; Yan, Z.; Samuel, E. L.; Natelson, D.; Tour, J. M. Iron Oxide Nanoparticle and Graphene Nanoribbon Composite as an Anode Material for High-Performance Li-Ion Batteries. Adv. Funct. Mater. 2014, 24, 2044−2048. (32) Zhu, X.; Zhu, Y.; Murali, S.; Stoller, M. D.; Ruoff, R. S. Nanostructured Reduced Graphene Oxide/Fe2O3 Composite as a High-Performance Anode Material for Lithium Ion Batteries. ACS Nano 2011, 5, 3333−3338. (33) Shi, Y.; Guo, B.; Corr, S. A.; Shi, Q.; Hu, Y.-S.; Heier, K. R.; Chen, L.; Seshadri, R.; Stucky, G. D. Ordered Mesoporous Metallic MoO2 Materials with Highly Reversible Lithium Storage Capacity. Nano Lett. 2009, 9, 4215−4220. (34) Laruelle, S.; Grugeon, S.; Poizot, P.; Dolle, M.; Dupont, L.; Tarascon, J. On the Origin of the Extra Electrochemical Capacity Displayed by MO/Li Cells at Low Potential. J. Electrochem. Soc. 2002, 149, A627−A634. (35) Xu, X.; Cao, R.; Jeong, S.; Cho, J. Spindle-like Mesoporous αFe2O3 Anode Material Prepared from MOF Template for High-Rate Lithium Batteries. Nano Lett. 2012, 12, 4988−4991. (36) Wang, B.; Chen, J. S.; Wu, H. B.; Wang, Z.; Lou, X. W. Quasiemulsion-Templated Formation of α-Fe2O3 Hollow Spheres with Enhanced Lithium Storage Properties. J. Am. Chem. Soc. 2011, 133, 17146−17148. (37) Zhang, L.; Wu, H. B.; Madhavi, S.; Hng, H. H.; Lou, X. W. Formation of Fe2O3 Microboxes with Hierarchical Shell Structures from Metal−Organic Frameworks and Their Lithium Storage Properties. J. Am. Chem. Soc. 2012, 134, 17388−17391. (38) Wang, R.; Xu, C.; Sun, J.; Gao, L. Three-Dimensional Fe2O3 Nanocubes/Nitrogen-Doped Graphene Aerogels: Nucleation Mechanism and Lithium Storage Properties. Sci. Rep. 2014, 4, 7171. (39) Cho, J. S.; Hong, Y. J.; Kang, Y. C. Design and Synthesis of Bubble-Nanorod-Structured Fe2O3−Carbon Nanofibers as Advanced Anode Material for Li-Ion Batteries. ACS Nano 2015, 9, 4026−4035. (40) Ma, R.; Wang, M.; Dam, D. T.; Yoon, Y. J.; Chen, Y.; Lee, J. M. Polyaniline-Coated Hollow Fe2O3 Nanoellipsoids as an Anode Material for High-Performance Lithium-Ion Batteries. ChemElectroChem 2015, 2, 503−507. (41) Lv, X.; Deng, J.; Wang, J.; Zhong, J.; Sun, X. Carbon-Coated αFe2O3 Nanostructures for Efficient Anode of Li-Ion Battery. J. Mater. Chem. A 2015, 3, 5183−5188. (42) Wang, Z.-L.; Xu, D.; Zhong, H.-X.; Wang, J.; Meng, F.-L.; Zhang, X.-B. Gelatin-Derived Sustainable Carbon-Based Functional Materials for Energy Conversion and Storage with Controllability of Structure and Component. Sci. Adv. 2015, 1, e1400035. (43) Li, Y.; Zhu, C.; Lu, T.; Guo, Z.; Zhang, D.; Ma, J.; Zhu, S. Simple Fabrication of a Fe2O3/Carbon Composite for Use in a HighPerformance Lithium Ion Battery. Carbon 2013, 52, 565−573. (44) Cao, K.; Jiao, L.; Liu, H.; Liu, Y.; Wang, Y.; Guo, Z.; Yuan, H. 3D Hierarchical Porous α-Fe2O3 Nanosheets for High-Performance Lithium-Ion Batteries. Adv. Energy Mater. 2015, 5, 1401421. (45) Xiao, L.; Wu, D.; Han, S.; Huang, Y.; Li, S.; He, M.; Zhang, F.; Feng, X. Self-Assembled Fe2O3/Graphene Aerogel with High Lithium Storage Performance. ACS Appl. Mater. Interfaces 2013, 5, 3764−3769. (46) Liang, Y.; Li, Y.; Wang, H.; Dai, H. Strongly Coupled Inorganic/ Nanocarbon Hybrid Materials for Advanced Electrocatalysis. J. Am. Chem. Soc. 2013, 135, 2013−2036.

7053
